I can't tell if the tide is coming or going

Colleen -- an observation spawned by sporadic afterthoughts:

S2 : some [crabs] ... have lost their inner/selves -- 'they' (in S2 line 3) refers, by implication, to the shells; so my reading is that the shells are lucky to have shed their shell(s). I may be wrong, but I think that passage needs modification so that 'they' refers to the inner selves rather than the shells.
I guess this stanza is the core of the poem -- the thread of association with weight loss suggests that the motivation goes beyond vanity, and addresses issues like self-worth, aspirations and perhaps even areas relating to social norms and prejudice. I don't know -- 'freedom' has many connotations, and I'm waffling, so time I moved out :>)